Ron Boyd¹, Gareth Chalmers², Claus Diessel²

(1) University of Newcastle, Callaghan, NSW, Australia
(2) University of Newcastle, Australia

ABSTRACT: The Signature Of Low Accommodation Terrestrial Stratigraphy - View From A Peat Bog

Interpretation and correlation of stratigraphy in terrestrial settings is difficult without the presence of interbedded marine units. It is particularly difficult in low accommodation settings in which only thin successions accumulate over long time intervals. One technique that holds the promise of successful terrestrial correlation and interpretation is that of coal seam characterisation. Not all coals are the same, and we characterise them in terms of their original mire ecosystem, and tendency to preserve either wetting-upward or drying-upward internal trends. These trends are determined petrographically from the seam composition of detrital minerals, macerals and dispersal indicators. Further characterisation comes from the style of peat initiation under either paludification or terrestrialisation conditions. The results reflect the relationship between peat accumulation and the position of the groundwater table. Hence this relationship can be interpreted in a sequence stratigraphic context, describing the interaction between sediment (peat) input and base (groundwater) level.

When this high resolution technique was applied to a field site in the Lloydminster region of the Cretaceous Western Canada Sedimentary Basin, it produced some surprising results. For locations less than 50 km apart, coal seams were discontinuous across the area. Individual wetting and drying upward cycles could not be correlated through the region, indicating either diachronous deposition of the same seam, or contrasting climatic and tectonic conditions over short distances. Confirmation of this interpretation was aided by corresponding contrasts in clastic composition and drainage geometries within the same time interval. Results indicate that this style of coal and clastic sediment deposition may be characteristic of low accommodation terrestrial settings.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado